1. Technical Field
The present invention relates to a piezoelectric actuator.
2. Related Art
A piezoelectric actuator is a driving device including a piezoelectric element that converts a driving voltage such as a high-frequency alternating-current voltage into mechanical vibration and a driven body driven by the piezoelectric element. As a form of the piezoelectric actuator, there is known a piezoelectric actuator including a rotor or a longitudinal member as the driven body (e.g., JP-A-2007-189900 (Patent Literature 1)). The piezoelectric actuator transmits bending vibration of the piezoelectric element via a projection, which projects from a vibrating body including the piezoelectric element, and rotates the rotor in a predetermined direction.
In the piezoelectric actuator described in Patent Literature 1, the projection of the vibrating body vibrates to draw an elliptical track. The piezoelectric actuator changes a vibration pattern of the vibrating body according to selection of an energization pattern to electrodes of the vibrating body and changes the direction of the vibration of the projection of the vibrating body. Consequently, the piezoelectric actuator can rotate the rotor in both the directions of a forward direction and a backward direction (counterclockwise and clockwise). In the piezoelectric actuator described in Patent Literature 1, the vibrating body is urged to the rotor by a coil spring.
Such a piezoelectric actuator attracts attention as a driving source for sections of robots such as joints of a robot. When the robot is taught, the piezoelectric actuator is stopped and force is applied from the outside to bend and stretch the joints of the robot.
However, in the piezoelectric actuator described in Patent Literature 1, when the robot is taught, since the piezoelectric actuator stops and the projection of the vibrating body is always in contact with the rotor, the rotor is braked. Therefore, it is necessary to apply force exceeding the retention of the brake to the rotor. When the driving source of the robot includes a reduction gear, larger force is necessary because of a reduction ratio of the reduction gear. For example, when the robot is taught, a delicate motion of manual feeling or the like with a technical skill, the manual feeling is less easily accurately transmitted if the retention is large.